Half-shield phase detection auto-focus sensor for auto-exposure convergence

ABSTRACT

Systems, apparatuses, and methods for using a half-shield phase detection auto-focus (PDAF) sensor for auto-exposure convergence are disclosed. A camera includes at least one or more half-shield PDAF sensors and control logic for performing an automatic exposure control convergence procedure. The control logic receives half-pixel values from half-shield PDAF sensors for a first frame. The control logic calculates twice the value of each half-pixel value captured by the half-shield PDAF sensors for the first frame. Then, the control logic adjusts an exposure setting used for capturing a second frame based on how much twice the value of each sensor value is over the maximum pixel intensity value. This approach allows the automatic exposure control convergence procedure to converge more quickly than prior art procedures.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to Provisional Patent Application Ser.No. 63/044,621, entitled “HALF-SHIELD PHASE DETECTION AUTO-FOCUS SENSORFOR AUTO-EXPOSURE CONVERGENCE”, filed Jun. 26, 2020, the entirety ofwhich is incorporated herein by reference.

BACKGROUND Description of the Related Art

When a camera is used in environments with different ambient lightintensities, the ideal exposure time varies according to the ambientlight intensity. For a bright light condition, a short exposure is usedto avoid the resultant image being overexposed. For a low lightcondition, a long exposure is used to avoid a dark image. Most camerasinclude an automatic exposure control mechanism to automatically adjustthe exposure settings based on the ambient light conditions. However,the time it takes for the automatic exposure control mechanism toconverge can result in a negative user experience if the shot-to-shottime or start-to-shot time is too long. The shot-to-shot time refers tothe time in between successive images captured by the camera, while thestart-to-shot time refers to the time it takes for the camera to capturean image from when the user activates the camera (i.e., presses theshutter button).

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages of the methods and mechanisms described herein may bebetter understood by referring to the following description inconjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram of one implementation of a camera.

FIG. 2 includes diagrams of histograms of the pixel intensity values fora given image.

FIG. 3 illustrates one example of a histogram of an over-exposed imageand corresponding exposure value corrections.

FIG. 4 is a block diagram of one implementation of a portion of an imagepixel array for use in a camera.

FIG. 5 is a block diagram of one implementation of an apparatus for usein a camera.

FIG. 6 is a generalized flow diagram illustrating one implementation ofa method for reducing a convergence time of an automatic exposure loop.

FIG. 7 is a generalized flow diagram illustrating one implementation ofa method for increasing an accuracy of adjustments to an exposure value.

FIG. 8 is a generalized flow diagram illustrating one implementation ofa method for using a half-shield phase detection auto-focus sensor forauto-exposure convergence.

FIG. 9 is a generalized flow diagram illustrating one implementation ofa method for using partially shielded sensors to help perform anauto-exposure loop.

FIG. 10 is a generalized flow diagram illustrating one implementation ofa method for performing an automatic exposure control convergenceprocedure.

FIG. 11 is a generalized flow diagram illustrating one implementation ofa method for generating a representative full-pixel value.

DETAILED DESCRIPTION OF IMPLEMENTATIONS

In the following description, numerous specific details are set forth toprovide a thorough understanding of the methods and mechanisms presentedherein. However, one having ordinary skill in the art should recognizethat the various implementations may be practiced without these specificdetails. In some instances, well-known structures, components, signals,computer program instructions, and techniques have not been shown indetail to avoid obscuring the approaches described herein. It will beappreciated that for simplicity and clarity of illustration, elementsshown in the figures have not necessarily been drawn to scale. Forexample, the dimensions of some of the elements may be exaggeratedrelative to other elements.

Various systems, apparatuses, and methods for using a half-shield phasedetection auto-focus (PDAF) sensor to optimize auto-exposure convergenceare disclosed herein. In one implementation, a camera includes aplurality of half-shield PDAF sensors used for performing an auto-focusroutine. These half-shield PDAF sensors can also be used to reduce theauto-exposure convergence time by generating a more accurateover-exposure estimate. For example, if a first frame is over-exposed,one or more half-pixel values are retrieved from one or more half-shieldPDAF sensors. The half-pixel values are doubled, and a representativedoubled half-pixel value is calculated based on these values. In oneimplementation, the representative doubled half-pixel value iscalculated as an average of the doubled half-pixel values. Next, therepresentative doubled half-pixel value is provided as an estimate ofthe over-exposure of the first frame to an auto-exposure controlmechanism. The exposure setting is adjusted for a second frame, wherethe adjustment is determined based on the estimate of the over-exposureof the first frame. Through the use of these techniques, a relativelyfast auto-exposure convergence time can be achieved. This helps toreduce the shot-to-shot time period as well as the start-to-shot timeperiod.

Referring now to FIG. 1, a diagram of one implementation of a camera 100is shown. In one implementation, camera 100 includes half-shield phasedetection auto-focus (PDAF) sensors for automatically adjusting thefocus of camera 100. Additionally, in one implementation, camera 100uses the half-shield PDAF sensors for automatically adjusting theexposure settings. Each half-shield PDAF sensor includes a half-shieldwhich blocks half of the incident light. Thus, luminance captured by ahalf-shield PDAF sensor is half of what an ordinary pixel sensor wouldcapture. If the luminance captured by half-shield PDAF sensor isdoubled, this gives a close approximation of what an ordinary pixelsensor would register. For regions of an image which are over-saturated,the ordinary pixel sensors will be at the maximum pixel intensity value(e.g., 1023 for a 10-bit pixel value). In one implementation, to attainan estimate of how over-saturated the image is, the luminance capturedby a half-shield PDAF sensor is doubled and then used as the estimate ofover-saturation.

For example, if an image is over-exposed, camera 100 generates anestimate of the amount of over-exposure based on doubling the half-pixelvalue captured from a given half-shield PDAF sensor. In some cases,camera 100 calculates an average of the luminance of a plurality ofhalf-shield PDAF sensor values. Then, camera 100 doubles the average anduses the doubled average as an estimate of the amount of over-exposureof the image. Next, camera 100 uses the estimate of over-exposure todetermine how much to reduce the exposure settings for the next image.This approach allows an automatic exposure control convergence procedureto converge more quickly than a traditional procedure. Accordingly,implementations for using a half-shield pixel value to estimate anover-exposure level of an image are described in the remainder of thisdisclosure. It is noted that any type of system or device can implementthe techniques described herein, including an integrated circuit (IC),processing unit, mobile device, computer, camera, wearable device, andother types of computing devices and systems. Also, while thedescriptions herein often refer to images, it should be understood thatthese descriptions also apply to video frames captured by a video cameraor other devices capable of capturing a sequence of images.

Turning now to FIG. 2, diagrams of histograms 200 and 205 for the pixelintensity values of a given image are shown. Histogram 200 shows thedistribution of 10-bit pixel values of an over-exposed image. In somecases, histogram 200 can be provided as an input to an automaticexposure control convergence procedure to enable the procedure todetermine how to adjust the exposure settings for capturing a subsequentimage. As shown in histogram 200, a relatively large number of pixelsare at the maximum pixel intensity value of 1023. This makes itdifficult to determine how much the given image has been overexposedsince the amount that the actual pixel intensity values are over themaximum value is unknown.

One way to address this issue is to use a larger number of bits perpixel. For example, histogram 205 on the right-side of FIG. 2 shows ahistogram for the same image but using 20-bits per pixel rather than10-bits per pixel. Accordingly, when 20-bit pixel values are used, thehistogram is spread out throughout the full range of pixel values ratherthan having a large percentage of pixel values being saturated. However,doubling the number of bits used per pixel value increases the hardwarecost and power consumption of the camera. Therefore, other solutions forprocessing over-exposed images are desired.

Referring now to FIG. 3, one example of a histogram 305 of anover-exposed image and corresponding exposure value corrections areshown. Histogram 305 represents one example of a histogram of pixelvalues for an over-exposed image. Since a relatively large percentage ofpixels are at the maximum pixel intensity, the actual distribution ofthese saturated pixels is unknown. The saturated pixels are representedby unknown area 310 in histogram 305. When histogram 305 is provided toan automatic exposure control convergence procedure, the automaticexposure control convergence procedure will guess what the distributionof the saturated pixels is so as to make a corresponding adjustment tothe exposure value (EV) applied to the next image.

As used herein, the term “exposure value” is defined as a parameterrepresenting the degree of exposure. In other words, the “exposurevalue” is the amount of exposure applied to an image through the variousexposure settings that are available for adjustment. Examples ofexposure settings include shutter speed, International Organization forStandardisation (ISO) speed, aperture size, exposure time, and/or otherparameters. As the exposure value is increased, the pixel intensity(i.e., luminance) of a corresponding captured image will increase. Asthe exposure value is decreased, the pixel intensity of a correspondingcaptured image will decrease. Adjusting the exposure value can involveadjusting any one or more of the exposure settings.

Histogram 315 shows the same pixel values for histogram 305 but with thedashed line to the right of the maximum pixel intensity valuerepresenting an estimate of the pixel distribution for the saturatedpixels. This estimate assumes that the saturated pixels have values muchhigher than the maximum pixel intensity value. If the automatic exposurecontrol convergence procedure assumes that the actual distribution lookslike that shown for the dashed line of histogram 315, the automaticexposure control convergence procedure will decrease the exposure valueby a relatively large amount (e.g., 3 EV). Histogram 320 shows anotherestimate of the pixel distribution for saturated pixels but with most ofthe pixels being only slightly more intense than the maximum pixelintensity value. If the automatic exposure control convergence procedureassumes that the actual distribution matches the dashed line ofhistogram 320, the automatic exposure control convergence procedure willdecrease the exposure value by a relatively small amount (e.g., 1 EV).

When an automatic exposure control convergence procedure processes apixel distribution with a relatively large number of saturated pixels,the automatic exposure control convergence procedure is unable to have aprecise understanding of how these saturated pixels are distributed.This results in a slow convergence and an unacceptable delay for theend-user of the camera. Some automatic exposure control convergenceprocedures take an aggressive approach to exposure value correction inresponse to detecting an over-exposed image. This can result in anovershoot and a relatively darker image as the next image if theexposure value is decreased too much, especially if the real pixeldistribution is similar to that shown in the dashed line of histogram320. Other automatic exposure control convergence procedures take aconservative approach to exposure value correction in response todetecting an over-exposed image. The result of a conservative approachis often a slow convergence, especially for pixel distributions similarto that shown for the dashed line of histogram 315. Accordingly, it isdesired to come up with improved techniques for estimating theover-exposure of images to help reduce the time needed for the automaticexposure control convergence procedure to converge.

Turning now to FIG. 4, a block diagram of one implementation of aportion of an image pixel array 400 for use in a camera is shown. Thegrid of pixels shown in FIG. 4 is a small cross-section of an imagepixel array 400 that is included within any of various types of cameradevices. The pattern shown in this grid can be repeated throughout theentirety of the overall image pixel array. As shown, a half-shield phasedetection auto-focus (PDAF) pixel is shown in the left-center of array400, with half-left window 402 open to allow in incident light. Theright-half of this pixel is opaque to block any incident light fromreaching the sensor underneath the pixel. Also, the half-shield PDAFpixel in the right-center of array 400 has a half-right window 404 opento allow in incident light. Any number of half-shield PDAF pixel pairswhich are constructed similar to the half-shield PDAF pixel pair ofhalf-left window 402 and half-right window 404 can be distributedthroughout the overall image pixel array.

The other pixels of pixel array 400 are regular pixels arranged in apattern of green, red, and blue pixels. Each green, red, and blue pixelis labeled with a G, R, and B, respectively. It should be understoodthat the pattern of regular pixels and half-shield PDAF pixels shown inpixel array 400 is merely indicative of one type of pattern that can beused in a given implementation. In other implementations, other patternsof regular pixels and half-shield PDAF pixels can be arranged within thepixel array.

Typically, the pixel values captured by half-shield PDAF pixels are usedto implement an auto-focus control procedure. However, in oneimplementation, the half-shield PDAF pixels are also used to implementan auto-exposure convergence procedure. In this implementation, controllogic receives the pixel values captured by the sensors underneathhalf-left window 402 and half-right window 404. The control logicgenerates a representative doubled half-pixel value based on the pixelvalues captured by the sensors underneath half-left window 402 andhalf-right window 404. The representative doubled half-pixel value isthen provided to the automatic exposure control convergence procedureand used to determine how much to adjust the exposure value for the nextimage.

For example, in one implementation, the representative doubledhalf-pixel value is calculated as the sum of the pixel values capturedby the sensors underneath half-left window 402 and half-right window404. In another implementation, the representative doubled half-pixelvalue is calculated as twice the value of one of the pixel valuescaptured by either the sensor underneath half-left window 402 or thesensor underneath half-right window 404. For example, in oneimplementation, the larger of the two pixel values is doubled and thenused as the representative doubled half-pixel value. In otherimplementations, other techniques for generating the representativedoubled half-pixel value can be utilized.

In one scenario, the pixels of pixel array 400 may capture values for anover-exposed image or for an over-exposed region of an image. The red,green, and blue pixels may all be at the maximum pixel intensity, suchas 1023 for 10-bit values. In this scenario, the values captured by thesensors under half-left window 402 and half-right window 404 may be lessthan 1023. For example, in one implementation, these values may be 800.This would indicate that the actual pixel values of the red, green, andblue pixels are closer to 1600. If the approximation of 1600 is providedto the automatic exposure control convergence procedure, this wouldallow the automatic exposure control convergence procedure to make theproper adjustment to the exposure settings to accurately reduce theover-exposure. As a result, this would allow the automatic exposurecontrol convergence procedure to converge more rapidly.

It is noted that the “half-shield pixel values” captured underneathhalf-left window 402 and half-right window 404 may not be exactly halfof what a normal pixel value in that location would be even though thesewindows are half-shielded. The relationship between the actualhalf-shield pixel values captured underneath half-left window 402 andhalf-right window 404 and the normal pixel values that would be capturedwithout any shielding depends on a specific type of image sensormanufacturing. While it is described in many cases that a half-shieldpixel value will be doubled to approximate what a normal pixel valuewould be, it should be understood that this represents one possibleimplementation. In another implementation, a calibration procedure isperformed to calculate the sensitivity difference between a half-shieldpixel and a regular pixel. Depending on the type of image sensor beingused, this sensitivity difference may be 1.9, 2.1, or some other value.This difference is then applied to generate a representative full-pixelvalue from one or more captured half-shield pixel values. Accordingly,it should be understood that the descriptions herein that recite“doubling a half-pixel value” are not limited to multiplying ahalf-shield pixel value by two, but can also cover other implementationswhere the sensitivity difference being applied is equal to some othervalue different from two. Also, “doubling a half-pixel value” can alsocover adding two half-pixel values together and then optionally applyinga correction factor to the sum of the two half-pixel values. Thiscorrection factor can be determined during a calibration process. Othertechniques for generating a representative full-pixel value from one ormore captured half-shield pixel values are possible and arecontemplated. Additionally, it is noted that the terms “representativedoubled half-pixel value” and “representative full-pixel value” can beused interchangeably herein.

Referring now to FIG. 5, a block diagram of one implementation of anapparatus 500 for use in a camera is shown. In one implementation,apparatus 500 includes at least pixel array 505, interface 515, controllogic 520, and exposure settings 525. Pixel array 505 includes regularpixels 507A-N and a plurality of half-shield phase detection auto-focus(PDAF) sensors 510A-N. It is noted that half-shield PDAF sensors 510A-Ncan also be referred to herein as half-shield PDAF pixel units 510A-N.Control logic 520 is coupled to pixel array 505 via interface 515.Interface 515 is representative of any type of interface for couplingthe values of half-shield PDAF sensors 510A-N to control logic 520. Itis noted that apparatus 500 can include any number of other componentsin addition to those shown in FIG. 5. In one implementation, apparatus500 is located within camera 100 of FIG. 1. In other implementations,apparatus 500 is located within a smartphone, tablet, computer, securitydevice, wearable device, or other types of systems or devices.

In one implementation, control logic 520 uses values from one or more ofhalf-shield PDAF sensors 510A-N to generate an estimate of theover-exposure of a given image. For example, in one implementation,control logic 520 calculates a luminance value from the half-shield PDAFsensor 510A-N. In one implementation, the luminance value “Y” iscalculated as Y=0.3*R+0.59*G+0.11*B, where R, G, and B are the red,green, and blue pixel half-shield PDAF sensor values, respectively. Inanother implementation, there is a clear color filter covering theunshielded half of the PDAF sensor, and the luminance value “Y” is setequal to the captured half-shield PDAF sensor value in this case. In afurther implementation, there is a green color filter covering theunshielded half of the PDAF sensor, and the luminance value “Y” is equalto the captured half-shield PDAF green pixel value. Otherimplementations can use other suitable techniques for calculating theluminance value based on the value(s) captured by one or morehalf-shield PDAF sensor(s).

Then, control logic 520 doubles each luminance value and then calculatesan average from the doubled values. In one implementation, control logic520 selects half-shield PDAF sensors 510A-N from over-exposed areas ofthe given image for generating the average from the doubled values. Theaverage of the doubled values is then used as the estimate of theover-exposure of the given image. Then, control logic 520 causes theexposure settings 525 applied to the next image to be adjusted to reducethe brightness of the next image based on the estimate of over-exposure.Exposure settings 525 include settings such as shutter speed, ISO speed,aperture size, exposure time, and/or other parameters.

In one implementation, the half-pixel values from the half-shield PDAFsensors are provided to an automatic focus procedure in parallel withbeing provided to the automatic exposure control convergence procedure.It is noted that depending on the implementation, the functionsdescribed as being performed by control logic 520 can be performed usingany combination of hardware and/or software. For example, in anotherimplementation, at least a portion of the functionality described asbeing performed by control logic 520 is performed by a processing unitexecuting program instructions.

Turning now to FIG. 6, one implementation of a method 600 for reducing aconvergence time of an automatic exposure loop is shown. For purposes ofdiscussion, the steps in this implementation and those of FIG. 7-10 areshown in sequential order. However, it is noted that in variousimplementations of the described methods, one or more of the elementsdescribed are performed concurrently, in a different order than shown,or are omitted entirely. Other additional elements are also performed asdesired. Any of the various systems or apparatuses described herein areconfigured to implement method 600.

One or more half-shield phase detection auto-focus (PDAF) pixel unitscapture half-pixel values for one or more pixel locations within a givenframe (block 605). It is noted that the half-pixel values may not beprecisely half of what a normal pixel value would be for an unshieldedpixel at the same location. However, for the purposes of variousdiscussion herein, the values captured under the half-shield pixel unitswill be referred to as “half-pixel” values. The half-pixel values mightbe some other fraction of a normal pixel value, and this fraction can bediscovered during a calibration process in one implementation. In someimplementations, the half-pixel values are considered to be half of anormal pixel value for approximation purposes until a calibrationprocess is performed.

Control logic receives one or more half-pixel values from the one ormore half-shield PDAF pixel units (block 610). The control logiccalculates a full-pixel value for each of the one or more half-pixelvalues (block 615). Then, the control logic provides a representativefull-pixel value as an input to an automatic exposure controlconvergence procedure (block 620). After block 620, method 600 ends. Theautomatic exposure control convergence procedure can then make accurateadjustments to the exposure settings based on the representativefull-pixel value. In one implementation, a magnitude of the adjustmentto the exposure setting is calculated based on the representativefull-pixel value. For example, method 800 of FIG. 8 describes an exampleof adjusting the exposure settings in accordance with oneimplementation. Other techniques for adjusting the exposure settingbased on the representative full-pixel value are possible and arecontemplated.

Depending on the implementation, the representative full-pixel value canbe calculated in different ways based on the one or more half-pixelvalues from the one or more half-shield PDAF pixel units. For example,in one implementation, the representative full-pixel value is calculatedas an average of the luminance of the one or more doubled half-pixelvalues from the one or more half-shield PDAF pixel units. In some cases,the average is calculated from only those half-pixel values which werecaptured in oversaturated locations within the given frame. In anotherimplementation, the representative full-pixel value is calculated as two(or some other factor which is determined during a calibration process)multiplied by the maximum half-pixel value of a plurality of half-pixelvalues from a plurality of half-shield PDAF pixel units.

Referring now to FIG. 7, one implementation of a method 700 forincreasing an accuracy of adjustments to an exposure value is shown.Control logic receives one or more values from the one or morehalf-shield PDAF sensors captured from a first frame (block 705). Thecontrol logic converts each value of the one or more values captured bythe one or more half-shield PDAF sensors of a first frame into a fullpixel value (block 710). Next, the control logic calculates arepresentative full-pixel value based on the full pixel values convertedfrom the values captured by the one or more half-shield PDAF sensors forthe first frame (block 715). In one implementation, the representativefull-pixel value is calculated as an average of the luminance of thefull-pixel values. In another implementation, the representativefull-pixel value is calculated from a single half-pixel sensor that islocated in an over-exposed area of the first frame. In a furtherimplementation, the representative full-pixel value is calculated as anaverage of doubled half-pixel luminance values from multiple pixellocations from over-exposed areas of the first frame. In oneimplementation, the over-exposed areas of the first frame are identifiedas regions having greater than a threshold percentage of saturated pixelvalues.

Then, the control logic uses the representative full-pixel value as anestimate of the over-exposure of the first frame (block 720). Next, thecontrol logic adjusts the exposure value used for a second frame basedon the estimate of the over-exposure of the first frame (block 725). Inone implementation, the control logic causes the exposure value to bereduced by an amount that is proportional to the estimate of theover-exposure of the first frame. After block 725, method 700 ends. Itis noted that method 700 can be performed any number of times until theauto-exposure algorithm converges. However, using method 700 allows theauto-exposure algorithm to converge more quickly than the prior artauto-exposure algorithms.

Turning now to FIG. 8, one implementation of a method 800 for using ahalf-shield phase detection auto-focus sensor for auto-exposureconvergence is shown. Control logic determines that a first framecaptured by a camera is over-exposed (block 805). Any suitable techniquefor determining that the first frame is over-exposed can be employed,with the technique varying according to the implementation. For example,in one implementation, the control logic determines that the first frameis over-exposed if greater than a threshold percentage (e.g., 20%) ofpixels of the first frame are saturated (i.e., at the maximum pixelintensity value). The threshold percentage can vary from implementationto implementation.

In response to determining that the first frame is over-exposed, thecontrol logic calculates a representative full-pixel value based onhalf-pixel values captured by one or more half-shield phase detectionauto-focus (PDAF) sensors for the first frame (block 810). For example,in one implementation, the control logic calculates the representativefull-pixel value by taking the average of double the half-pixel valuescalculated from the one or more half-shield PDAF sensors. In otherimplementation, other suitable techniques for calculating therepresentative full-pixel value based on the pixel values from one ormore half-shield PDAF sensors can be employed.

If the amount that the representative full-pixel value is greater thanthe maximum pixel intensity value is more than a first threshold(conditional block 815, “yes” leg), then the control logic determines ifthe representative full-pixel value is greater than the maximum pixelintensity value by more than a second threshold (conditional block 820).It is assumed for the purposes of this discussion that the secondthreshold is greater than the first threshold. If the amount that therepresentative full-pixel value is greater than the maximum pixelintensity value is less than the first threshold (conditional block 815,“no” leg), then the control logic causes the exposure value to decreaseby a first amount when capturing a second frame (block 825). It isassumed for the purposes of this discussion that the second frame iscaptured subsequent to the first frame.

If the representative full-pixel value is greater than the maximum pixelintensity value by less than the second threshold (conditional block820, “no” leg), then the control logic causes the exposure value todecrease by a second amount for capturing the second frame, where thesecond amount is greater than the first amount (block 830). If therepresentative full-pixel value is greater than the maximum pixelintensity value by more than the second threshold (conditional block820, “yes” leg), then the control logic causes the exposure value todecrease by a third amount when capturing the second frame, where thethird amount is greater than the second amount (block 835). After blocks825, 830, and 835, method 800 ends. While method 800 describes using twothreshold values for comparison purposes, it is noted that otherimplementations can have other numbers of thresholds for comparing tothe representative full-pixel value. Increasing the number of thresholdsallows the control logic to adjust the exposure value at a finergranularity.

Referring now to FIG. 9, one implementation of a method 900 for usingpartially shielded sensors to help perform an auto-exposure loop isshown. Control logic receives one or more partial pixel values from theone or more partially shielded PDAF sensors captured from a first frame(block 905). The partially shielded PDAF sensors can be 75% shielded,87.5% shielded, 90% shielded, or other percentage amounts shielded withthe amount varying from implementation to implementation.

The control logic multiplies each value of the one or more values fromthe one or more partial pixel values by a factor to account for aportion that is un-shielded (block 910). For example, if the sensor is ¼un-shielded, then the control logic multiplies the corresponding partialpixel value by 4 or other value determined by a calibration process. Or,if the sensor is ⅛ un-shielded, then the control logic multiplies thecorresponding partial pixel value by 8 or other value determined by acalibration process. It is noted that the term “factor” can also bereferred to herein as a “sensitivity difference”. Next, the controllogic calculates a representative full pixel value based on thereconstituted pixel values (i.e., the one or more partial pixel valuesmultiplied by corresponding factors) (block 915). In one implementation,the representative full pixel value is calculated as an average of thereconstituted pixel values.

Then, the control logic uses the representative full pixel value as anestimate of the over-exposure of the first frame (block 920). Next, thecontrol logic adjusts an exposure value used for a second frame based onthe estimate of the over-exposure of the first frame (block 925). Afterblock 925, method 900 ends. It is noted that method 900 can be performedany number of times until the auto-exposure algorithm converges. Itshould be understood that while many of the examples provided in thisdisclosure describe the use of half-shield PDAF sensors, the scenariosdepicted in these examples can also be implemented withpartially-shielded PDAF sensors. When using partially-shielded PDAFsensors rather than half-shield PDAF sensors, appropriate adjustmentscan be made to the correction factors being applied to the capturedpartial-pixel values.

Turning now to FIG. 10, one implementation of a method 1000 forperforming an automatic exposure control convergence procedure is shown.A histogram of pixel intensity values are captured for a first image(block 1005). If greater than a threshold number of pixel intensityvalues are saturated (i.e., equal to the maximum pixel intensity value)(conditional block 1010, “yes” leg), then one or more half-shield PDAFpixel values are provided as an input to the automatic exposure controlconvergence procedure (block 1015). When providing half-shield PDAFpixel values to the automatic exposure control convergence procedure,these values are identified as being half-shield PDAF pixel values. Forcases when the automatic exposure control convergence procedure alsoreceives the regular pixel values for the over-exposed image, theautomatic exposure control convergence procedure will be able todifferentiate which values are generated by which sensor types to beable to make better adjustments to the exposure settings to achievefaster convergence.

If less than the threshold number of pixel intensity values aresaturated (i.e., equal to the maximum pixel intensity value)(conditional block 1010, “no” leg), then only regular pixel values(i.e., not including any of the half-shield PDAF pixel values) areprovided as an input to the automatic exposure control convergenceprocedure (block 1020). Next, the automatic exposure control convergenceprocedure adjusts the exposure settings for a second image based on theprovided pixel values (block 1025). After block 1025, method 1000 ends.

Referring now to FIG. 11, one implementation of a method 1100 forgenerating a representative full-pixel value is shown. A system orapparatus performs a calibration procedure to calculate a sensitivitydifference between a half-shield PDAF sensor and a regular unshieldedpixel sensor for a given camera (block 1105). The sensitivity differencespecifies a difference between values captured by a half-shield PDAFsensor and values captured by a regular unshielded pixel sensor. Anytype of calibration procedure can be performed in block 1105, with thetype of calibration procedure varying from implementation toimplementation.

Next, one or more sensitivity difference values (corresponding to thesensitivity difference) are provided to control logic of the givencamera (block 1110). In one implementation, the sensitivity differencevalue(s) are specified and provided as one or more values in asingle-precision floating point format. In another implementation, thesensitivity difference value(s) are specified and provided as one ormore values in a double-precision floating point format. In otherimplementations, the sensitivity difference value(s) are provided asvalue(s) in any of various other types of formats. In oneimplementation, the sensitivity difference can be stored in a memorydevice of the given camera, with the memory device accessible by thecontrol logic. In another implementation, the sensitivity difference isprovided to the control logic by software during run-time. Then, thecontrol logic applies the sensitivity difference value(s) to one or morecaptured half-pixel values to generate a representative full-pixel value(block 1115).

In one implementation, the control logic multiplies a sensitivitydifference value by each captured half-pixel value in block 1115. Inthis implementation, the sensitivity difference value is a single value.In another implementation, there are multiple sensitivity differencevalues, one for each range of half-pixel values. For example, in oneimplementation, if the half-pixel value is in the range of 401 to 500,then apply a first sensitivity difference value. If the half-pixel valueis in the range of 501 to 600, then apply a second sensitivitydifference value, if the half-pixel value is in the range of 601 to 700,then apply a third sensitivity difference value, and so on. The numberand size of ranges and the number of sensitivity difference values canvary according to the implementation. In a further implementation, thesensitivity difference is specified as a formula such as Y=A*x+b, whereY is the representative full-pixel value, x is the half-pixel value, andA and b are constants provided to the control logic. In otherimplementations, the sensitivity difference value(s) can be applied tothe one or more captured half-pixel values in other suitable manners. Itis noted that block 1115 can be performed any number of times by thecontrol logic using the sensitivity difference generated by thecalibration procedure. In some cases, the sensitivity difference can beperiodically updated and recalibrated by a new calibration procedure.After block 1115, method 1100 ends.

In various implementations, program instructions of a softwareapplication are used to implement the methods and/or mechanismsdescribed herein. For example, program instructions executable by ageneral or special purpose processor are contemplated. In variousimplementations, such program instructions are represented by a highlevel programming language. In other implementations, the programinstructions are compiled from a high level programming language to abinary, intermediate, or other form. Alternatively, program instructionsare written that describe the behavior or design of hardware. Suchprogram instructions are represented by a high-level programminglanguage, such as C. Alternatively, a hardware design language (HDL)such as Verilog is used. In various implementations, the programinstructions are stored on any of a variety of non-transitory computerreadable storage mediums. The storage medium is accessible by acomputing system during use to provide the program instructions to thecomputing system for program execution. Generally speaking, such acomputing system includes at least one or more memories and one or moreprocessors configured to execute program instructions.

It should be emphasized that the above-described implementations areonly non-limiting examples of implementations. Numerous variations andmodifications will become apparent to those skilled in the art once theabove disclosure is fully appreciated. It is intended that the followingclaims be interpreted to embrace all such variations and modifications.

What is claimed is:
 1. An apparatus comprising: an interface; andcontrol logic configured to: receive, via the interface, one or morehalf-pixel values captured by one or more half-shield phase detectionauto-focus (PDAF) sensors for a first image; calculate a representativefull-pixel value from the one or more half-pixel values; generate anestimate of an over-exposure of the first image based on therepresentative full-pixel value; and cause an adjustment to be made toone or more exposure settings used for capturing a second image, whereinthe adjustment is determined based on the estimate of the over-exposureof the first image.
 2. The apparatus as recited in claim 1, wherein thecontrol logic is further configured to cause the adjustment to be madeto one or more exposure settings to reduce a luminance of the secondimage by a given amount.
 3. The apparatus as recited in claim 1, whereinthe representative full-pixel value is calculated as a sum of ahalf-left pixel value and a half-right pixel value from a singlehalf-shield PDAF pixel pair.
 4. The apparatus as recited in claim 1,wherein the representative full-pixel value is calculated as double anaverage of a plurality of half-pixel values.
 5. The apparatus as recitedin claim 4, wherein the plurality of half-pixel values are selected froman oversaturated region of the first image.
 6. The apparatus as recitedin claim 1, wherein a magnitude of the adjustment is calculated based ona difference between the representative full-pixel value and a maximumpixel intensity value, and wherein the control logic is configured tocompare the difference to one or more thresholds to determine how muchto adjust an exposure value used for capturing the second image.
 7. Theapparatus as recited in claim 1, wherein the control logic is furtherconfigured to: receive a sensitivity difference value which specifies adifference between values captured by a half-shield PDAF sensor and aregular unshielded pixel sensor, wherein the sensitivity differencevalue is calculated during a calibration process; and apply thesensitivity difference value to the one or more one or more half-pixelvalues to generate the representative full-pixel value.
 8. A systemcomprising: one or more half-shield phase detection auto-focus (PDAF)sensors; and control logic configured to: receive one or more half-pixelvalues captured by the one or more half-shield PDAF sensors for a firstimage; calculate a representative full-pixel value from the one or morehalf-pixel values; generate an estimate of an over-exposure of the firstimage based on the representative full-pixel value; and cause anadjustment to be made to one or more exposure settings used forcapturing a second image, wherein the adjustment is determined based onthe estimate of the over-exposure of the first image.
 9. The system asrecited in claim 8, wherein the control logic is further configured tocause the adjustment to be made to one or more exposure settings usedfor capturing the second image to reduce a luminance of the second imageby a given amount.
 10. The system as recited in claim 8, wherein therepresentative full-pixel value is calculated as a sum of a half-leftpixel value and a half-right pixel value from a single half-shield PDAFpixel pair.
 11. The system as recited in claim 8, wherein therepresentative full-pixel value is calculated as double an average of aplurality of half-pixel values.
 12. The system as recited in claim 11,wherein the plurality of half-pixel values are selected from anoversaturated region of the first image.
 13. The system as recited inclaim 8, wherein a magnitude of the adjustment is calculated based on adifference between the representative full-pixel value and a maximumpixel intensity value, and wherein the control logic is configured tocompare the difference to one or more thresholds to determine how muchto adjust an exposure value used for capturing the second image.
 14. Thesystem as recited in claim 8, wherein the control logic is furtherconfigured to: receive a sensitivity difference value which specifies adifference between values captured by a half-shield PDAF sensor and aregular unshielded pixel sensor, wherein the sensitivity differencevalue is calculated during a calibration process; and apply thesensitivity difference value to the one or more one or more half-pixelvalues to generate the representative full-pixel value.
 15. A methodcomprising: receiving one or more half-pixel values captured by one ormore half-shield phase detection auto-focus (PDAF) sensors for a firstimage; calculating a representative full-pixel value from the one ormore half-pixel values; generating an estimate of an over-exposure ofthe first image based on the representative full-pixel value; andcausing an adjustment to be made to one or more exposure settings usedfor capturing a second image, wherein the adjustment is determined basedon the estimate of the over-exposure of the first image.
 16. The methodas recited in claim 15, cause the adjustment to be made to one or moreexposure settings reduce a luminance of the second image by a givenamount.
 17. The method as recited in claim 15, wherein therepresentative full-pixel value is calculated as a sum of a half-leftpixel value and a half-right pixel value from a single half-shield PDAFpixel pair.
 18. The method as recited in claim 15, wherein therepresentative full-pixel value is calculated as double an average of aplurality of half-pixel values.
 19. The method as recited in claim 18,wherein the plurality of half-pixel values are selected from anoversaturated region of the first image.
 20. The method as recited inclaim 15, wherein a magnitude of the adjustment is calculated based on adifference between the representative full-pixel value and a maximumpixel intensity value.